*Edit: This game in fact plays and looks like Black Ops 1. Even then, the physics and movement isn't as good as that game.
I'm not giving this game a bad rating because I'm anti CoD. I have played and loved almost every CoD over the past 15 years or so. This game was released before it was finished or even okay tested. Obvious little bugs that play testing would have revealed, are simply everywhere. Gun models breaking, gun models floating into your head, scopes not rendering, players getting stuck on objects, etc. The list goes on. However, the game engine itself is terrible. It consistently drops frames, lags, and makes feels very slow and clunky. The gameplay certainly suffers because of it. I have played games with only knife getting well into the top of leaderboard on the largest game modes on the biggest maps simply because most players can't be competitive. This game isn't broken, it's not finished. This game is about 70% completed. Zombies was clearly made by a separate team but the engine still somewhat suffers the same fate. One thing I will say about zombies is that it is way too easy. They make the game artificially hard by adding more and more boss zombies as opposed to making zombies faster and harder to kill. The game is trivial. It's not fun. The Easter egg took about 2 days of a few hours of gameplay to learn and master and since then the replay value has fallen off completely.
TLDR: engine not good, game unfinished, zombies is ok but same engine issues, and zombies isn't hard